1. Field
The present disclosure relates to an apparatus for attaching substrates and a gap control unit thereof.
2. Background
An apparatus for attaching substrates is used to attach two substrates of a flat panel display device to each other. The thin panel display device could be thin film transistor liquid crystal display (TFT-LCD) panel, a plasma display panel (PDP), an OLED or some other type of display device.
A TFT-LCD device typically includes, a TFT substrate on which a plurality of TFTs (thin film transistors) are formed in a matrix, and a color filter substrate on which a color filter or a light shielding film is formed. The two substrates oppose each other and are attached to each other with a gap of a few micrometers.
The substrate attachment is performed by first aligning the substrates with respect to each other, attaching them to each other, and then pressing the two substrates together using pressure. An apparatus for attaching substrates typically includes a first chamber and a second chamber spaced apart from the first chamber. An inside surface of each chamber is provided with an electrostatic chuck (ESC) for holding the substrates before the attachment. The upper chamber may also include a vacuum chuck as well.
During the attachment process, the two substrates are carried into the apparatus and they are mounted on the upper and lower chambers. The first and the second chambers come together to form a sealed attaching space. The sealed attaching space is then vacuum exhausted by a pump so as to form a vacuum state in the inside thereof. A sealing member is provided between the first and the second chambers to maintain the vacuum in the sealed attaching space. The substrates are then aligned with each other, and the two substrates are attached to each other.
The attachment of the two substrates is performed only after the two substrates have been brought closely adjacent to each other. The substrates must be brought into close proximity to precisely align them, which is very important to the quality of the resulting display device.
When the substrates are brought close to each other, the above mentioned seal member is used to maintain the vacuum in the sealed attaching space. The sealing member also helps to control the gap between the substrates when they are in close proximity to each other, and before the attachment. The gap between the substrates can be determined by a depression amount of the seal member.
Another important factor in the apparatus for attaching substrates is the ability to perform horizontal movements of one or both chambers to properly align the substrates. In a conventional apparatus for attaching substrates, the gap maintenance and the horizontal movement are performed separately while maintaining the vacuum state. However, when these processes are performed sequentially, it takes a long time to accomplish the entire process.